Difeel: Biotin Conditioner For Hair Growth Grow thicker, longer, and fuller hair with the Difeel Biotin Pro-Growth Conditioner. Paired with the Pro-Growth Shampoo, this formula is perfect for thinning, dry, and damaged hair. Biotin is essential to hair health and growth, as it strengthens and fortifies the hair. While promoting healthy hair growth, this conditioner will make hair more vibrant, manageable, soft, and shiny.